Instability of shoulder arthroplasty: balancing mobility and stability.

Avoidance of instability after shoulder arthroplasty is based on an appreciation of normal articular anatomy and its restoration, as well as adequate soft tissue release and secure repair of subscapularis. Errors in restoration of articular anatomy, or disruption of soft tissues about the joint, are the principal reasons for instability. Revision in such cases can be challenging because of difficulties in restoring normal articular position and orientation, as well as reconstruction of deficient soft tissues.